Revenue is recognized when control of the promised goods or services is transferred to the Company’s customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. The Company assesses collectability based on the credit worthiness of the customer and past transaction history. The Company performs on-going credit evaluations of customers and generally does not require collateral from customers.

The Company sells its products primarily to customers in the semiconductor capital equipment industry. The Company’s revenues are highly concentrated, and we are therefore highly dependent upon a small number of customers. Typical payment terms with our customers range from thirty to sixty days.

The Company’s most significant customers (having accounted for 10% or more of sales) and their related sales as a percentage of total sales were as follows:

	Three Months Ended						Six Months Ended
	June 28,			June 29,			June 28,			June 29,
	2019			2018			2019			2018
Lam Research Corporation		40.8	%		61.9	%		40.3	%		64.2	%
Applied Materials, Inc.		19.5			21.6			20.2			21.5
Total		60.3	%		83.5	%		60.5	%		85.7	%

Three customers’ accounts receivable balances, Lam Research Corporation, Applied Materials, Inc. and ASM International, Inc., were individually greater than 10% of accounts receivable as of June 28, 2019 and December 28, 2018, in the aggregate approximately 62.3% and 62.9% of accounts receivable, respectively.

The Company provides warranty on its products for a period of up to two years and provides for warranty costs at the time of sale based on historical activity. Determination of the warranty reserve requires the Company to make estimates of product return rates and expected costs to repair or replace the products under warranty. If actual return rates and/or repair and replacement costs differ significantly from these estimates, adjustments to recognize additional cost of sales may be required in future periods. The warranty reserve is included in other current liabilities on the Condensed Consolidated Balance Sheets and are not considered significant.

The Company’s products are manufactured at our facilities in the U.S.A., China, Singapore and the Czech Republic. The Company provides services from operations in the U.S.A., Singapore, United Kingdom, Israel, Taiwan, South Korea, and China. Sales to customers are initiated through a purchase order and are governed by our standard terms and conditions, written agreements, or both. Revenue is recognized when performance obligations under the terms of an agreement with a customer are satisfied; generally, this occurs with the transfer of control of the products or when the Company provides the services. Transfer of control occurs at a specific point-in-time. Based on the enforceable rights included in our agreements or prevailing terms and conditions, products produced by the Company without an alternative use are not protected by an enforceable right of payment that includes a reasonable profit throughout the duration of the agreement. Sales with terms f.o.b. shipping point are recognized at the time of shipment. For sales transactions with terms f.o.b. destination, revenue is recorded when the product is delivered to the customer’s site. Consignment sales are recognized in revenue at the earlier of the period that the goods are consumed or after a period of time subsequent to receipt by the customer as specified by terms of the agreement, provided control of the promised goods or services has transferred.

Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods or providing services. Sales, value-add, and other taxes we collect concurrent with revenue-producing activities are excluded from revenue. Certain of our customers may receive cash-based incentives, such as rebates or credits, which are accounted for as variable consideration. We estimate these amounts based on the expected amount to be provided to customers and reduce revenues recognized. As of June 28, 2019, an accrual for unpaid customer rebates of $0.3 million is included in accrued expenses on the Company’s Condensed Consolidated Balance Sheet.

The following table presents the Company's revenues disaggregated by revenue segments (in thousands):

	Three Months Ended				Six Months Ended
	June 28,		June 29,		June 28,		June 29,
	2019		2018		2019		2018
Semiconductor Products and Solutions	$	210,390	$	290,213	$	410,635	$	605,055
Semiconductor Services Business		54,977		—		114,873		—
Total	$	265,367	$	290,213	$	525,508	$	605,055

The Company’s principal markets include America, Asia and Europe. The Company’s foreign operations are conducted primarily through its subsidiaries in China, Singapore, Israel, Taiwan, South Korea, United Kingdom and the Czech Republic. Sales by geographic area represent sales to unaffiliated customers and are based upon the location to which the products were shipped or services performed. The following table sets forth revenue by geographic area (in thousands):

	Three Months Ended				Six Months Ended
	June 28,		June 29,		June 28,		June 29,
	2019		2018		2019		2018
United States	$	133,000	$	159,187	$	270,254	$	343,962
China		12,422		16,812		20,430		18,978
Singapore		75,881		82,904		144,153		185,537
Austria		10,308		16,393		24,583		29,929
Korea		17,733		—		36,119
Other		16,023		14,917		29,969		26,649
	$	265,367	$	290,213	$	525,508	$	605,055